A pressure sensor device may generally include a sensor unit having a sensor element arranged in a casing with an opening in one surface thereof for measuring the pressure on the outside of the casing. The sensor unit is mounted on a mounting member such as a circuit board.
As such a pressure sensor device, a semiconductor pressure sensor comprising, for example, a pressure sensor unit accommodated in an opening of a casing which is mounted on a mounting member such as a circuit board via lead frames provided for the casing (see, for example, JP-A-10-90095) has been conceived.
The present inventors have discovered that a pressure sensor device configured as above is accompanied by the following problems. FIG. 7 is a sectional view schematically illustrating an exemplary related art semiconductor pressure sensor.
The sensor element 20 comprises a silicon chip 21 that produces an electric signal depending upon the pressure. The silicon chip 21 is secured onto a bed plate 22 such as glass. The sensor element 20 is secured by being accommodated in an opening 11 of a casing 10. The casing 10 is provided with lead frames 12 as lead members, and the sensor element 20 is electrically connected to the lead frames 12 through the bonding wires 23.
A sensor unit 40 is mounted on a mounting member 30 with an opening 11 in the casing 10 being faced to the side opposite to the mounting member 30, and is secured thereto by soldering or the like via the lead frames 12.
In the pressure sensor device, a closure 100 is mounted on the casing 10 so as to cover the opening 11 of the casing 10. The closure 100 is provided with a hole 101 for introducing the external pressure to the sensor element 20.
The closure 100 is provided for the reasons described below. First, in the step of assembling the pressure sensor device as illustrated in FIG. 8A, an adhering surface must be maintained for a mounting device K1 at the time of mounting the sensor unit 40 on the mounting member 30. The mounting device K1 operates to adhere the sensor unit 40 by utilizing a sucking force to pick it up from a pallet K2, and to mount it on the mounting member 30. Here, a closure 100 is necessary to serve as an adhering surface of the sensor unit 40 for the mounting device K1.
Second, the closure 100 is necessary for preventing the sensor element 20 from being erroneously operated by light. For example, when the sensor element 20 comprises a semiconductor such as silicon, irradiation with intense external light excites electrons in the semiconductor, thereby causing the output of the sensor element to fluctuate. As shown in FIG. 8B, the closure 100 is provided to suppress the incidence of light.
Because this pressure sensor device must include the closure 100, there is an increase in costs related to the closure 100 itself and assembling the closure 100.
Also, such a pressure sensor device including a closure may still fail to prevent passage of external light because it is likely that the external light may directly pass through the hole 101 of the closure 100 as shown in FIG. 8B and still cause erroneous operation.